Melatonin Receptor

Melatonin Production in...Bacteria (PubMed) 

Abstract only online.  I have PDF. 
This study is the second to demonstrate the presence of melatonin at the prokaryotic level, supporting the evidence that melatonin appeared very early in evolution. Its function in prokaryotes has not been determined, but may relate to its antioxidative actions.

Melatonin (Wiki) 
"Melatonin (pronounced /ˌmɛləˈtoʊnɪn/ ( listen)), also known chemically as N-acetyl-5-methoxytryptamine,[1] is a naturally occurring compound found in animals, plants, and microbes.[2][3] In animals, circulating levels of the hormone melatonin vary in a daily cycle, thereby allowing the entrainment of the circadian rhythms of several biological functions.[4]

Many biological effects of melatonin are produced through activation of melatonin receptors,[5] while others are due to its role as a pervasive and powerful antioxidant,[6] with a particular role in the protection of
nuclear and mitochondrial DNA.[7]

In mammals, melatonin is secreted into the blood by the pineal gland in the brain. Known as the "hormone of darkness", it is secreted in darkness in both day-active (diurnal) and night-active (nocturnal) animals.[8]

Lamellar Body = Pineal Gland.